1. Field of the Invention
This invention relates to pneumatic tires, particularly, high-speed performance pneumatic tires applicable to continuous use under high temperature conditions, which have a rubber composition excellent in heat resistance arranged in the tread thereof.
2. Related Art Statement
As a result of a rise, to a great extent, of the working temperature of tires due to a recent increase in the speed of automobiles, a further improvement in durability of tires has been earnestly desired, aiming at prevention of heat deterioration of the physical properties of rubber due to high temperatures.
Previously, as a process for preventing heat deterioration, a rubber composition low in heat build-up has been used which barely allows the temperature of the tire to rise. However, such a process is naturally limited insofar since rubber is a viscoelastic body. Alternatively, as another technique, there has been proposed a process to increase monosulfide bonds having a relatively high resistance to heat, in crosslinkages, or the like. However, its effect has not been sufficient.
In addition, providing starting materials of a high molecular weight substance with desired characteristics by chemically modifying the high molecular weight substance itself has been actively conducted as an industrially effective measure. For example, Japanese Patent Application Laid-open No. 52-71,590, describes that a rubber of a conjugated diene based polymer is modified by adding a polymerizable unsaturated monomer to unsaturated bonds thereof and the resulting modified rubber is then utilized as an adhesive, coating or photosensitive agent by subjecting it to a curing reaction by means of a free-radical initiator, ultraviolet rays or the like. However, no description is made of availability of such a modified rubber as a material for tires, particularly, a heat resistant material for tires.
Furthermore, Japanese Patent Application Laid-open No. 58-13,677 describes an anaerobic adhesive composition comprising a polymer having a methacryloyloxy group or acryloyloxy group on the side chain thereof and a polymerizable organic acid. However, similar to the method described above, no description is made of utilizing the composition as a heat resistant material for tires.